1. Technical Field
The present invention relates to a seismic isolation apparatus which does not burden the environment and which features damping characteristics better than prior art.
2. Description of the Related Art
Heretofore, seismic isolation apparatuses which are disposed between buildings and ground that supports the buildings, for reducing shaking due to earthquakes, have been known. In such a seismic isolation apparatus, in addition to a rubber body which serves as a resilient body, a damping alloy for mitigating vibrations associated with the shaking is incorporated. By compound action of these members, shaking due to earthquakes is mitigated, and earthquake shaking is less likely to be propagated to the building.
However, a lead material is commonly employed as the damping alloy of a conventional seismic isolation apparatus, in consideration of damping characteristics thereof. With concern for environmental aspects having become an important consideration in recent years, substitution of lead materials with other materials is being investigated.
Accordingly, a seismic isolation apparatus in which, in place of a damping alloy formed of a lead material, for example, a twin crystal alloy is processed into the form of a coil spring and incorporated in a rubber member has been considered. However, with a seismic isolation apparatus which simply employs a coil spring of a twin crystal alloy, when a horizontal direction displacement is applied to the seismic isolation apparatus, on the first occasion of displacement, an internal coil spring 122 is twisted in vicinities of two end portions thereof, as shown in FIG. 5B, and is crushed along a direction of a displacement X. As a result, it is not possible to maintain stable damping capabilities, and satisfactory damping effects are not obtained.
Accordingly, a seismic isolation apparatus with a structure in which a resin material fills the inside of a coil spring so as to obtain satisfactory damping effects, and the seismic isolation apparatus of Japanese Patent Application Laid-Open (JP-A) No. 11-270621 (JPA '621) and suchlike have been considered. The seismic isolation apparatus of JPA '621 has structure in which, instead of a damping alloy formed of a lead material, an ordinary coil spring in which, for example, a cross-sectional shape of a wire material thereof is formed to be circular, is inserted into a rubber laminate so as to provide satisfactory damping effects, and attenuation forces are generated.
Hence, a necessity has arisen to develop a component that does not burden the environment and that has damping characteristics equivalent to or better than conventional damping alloys, to serve as a damping alloy to be employed in seismic isolation apparatuses. However, with a seismic isolation apparatus in which a resin material fills the inside of a coil spring, or the seismic isolation apparatus of JPA '621 or the like, the coil spring that is used instead of a damping alloy is not capable of properly following displacements. Therefore, in accordance with crushing of the coil spring that is caused by rotation forces within the rubber body, there is an effect that generated forces are large, particularly at displacement limit points, and satisfactory damping characteristics have not been obtained after all.
Further, a necessity has arisen to develop a component that does not burden the environment and that has damping characteristics equivalent to or better than conventional damping alloys, to serve as a damping alloy to be employed in seismic isolation apparatuses. However, with the seismic isolation apparatus of JPA '621, in which an ordinary coil is employed with the cross-sectional shape of the wire material being a circular form, attenuation amounts of required magnitudes are not sufficiently obtained.
Accordingly, making a wire diameter, which is a diameter of the wire material of the coil spring, larger in order to increase attenuation amounts has been considered. However, if the wire diameter is simply made larger, stiffness increases and is excessive, and there is a risk of breaking laminated sheets which are disposed at an outer peripheral side of the coil spring to serve as the structural component of laminated rubber.
When an ordinary coil spring is employed, the coil spring deforms in accordance with the application of horizontal direction displacements to the seismic isolation apparatus. However, on the occasion of, for example, a first large displacement, there has been a risk of rotation forces being generated within the rubber laminate and the coil spring being crushed. Thus, when the coil spring in the seismic isolation apparatus has been crushed and has collapsed because of a large displacement, attenuation forces that are generated by the seismic isolation apparatus are reduced. Hence, it is not possible to maintain stable damping capabilities, and satisfactory damping effects are not obtained.